Ignition system



May 3, 1966 B. H. SHORT 3,249,808

" IGNITION SYSTEM Filed Sept 21. 1961 Q g IN VEN TOR Brooks f2. 8220;?

" QIR.M

a): ATTORNEY United States Patent 3,249,808 IGNITION SYSTEM Brooks H.Short, Anderson, Ind., assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed Sept. 21, 1961, Ser. No. 139,79312 Claims. (Cl. 315219) This invention relates to ignition systems forinternal combustion engines and more particularly to ignition systemswherein the current flow through the primary winding of an ignition coilis maintained substantially constant.

It iswell knownthat the voltage available to energize the primarycircuit of an ignition system on a motor vehicle varies widely underdifferent conditions of operation. Thus, during cranking of the engine,the available voltage drops and this drop is variable depending upon thetemperature where cranking occurs. This available voltage, of course,rises upon termination of cranking of the engine and then rises furtherwhen the engine begins running and drives the generator. The availablevoltage, of course, also varies with the condition of charge ofthebattery on the motor vehicle.

In conventional ignition systems, wherein breaker contacts controlcurrent flow through the primary circuit of the ignition system, it hassometimes been the practime to provide a resistor in the primary circuitwhich is shorted out of the primary circuit when cranking occurs. Atypical system of this type is shown in the patents to Leece 1,214,555and to Mallory 1,769,150. Although, systems of this type compensate forthe drop in voltage due to cranking of the engine, there is no finecontrol of primary circuit current, and there is no compensation ofprimary current under the many conditions other than cranking wheresystem voltage varies.

It accordingly is an object of this invention to provide an ignitionsystem wherein primary circuit current flow is maintained substantiallyconstant with changes in system voltage and without regard to the causeof such changes.

Another object of this invention is to provide an electronic switchmeans that controls current flow in the primary circuit of an ignitionsystem and wherein means are provided to maintain the current flowthrough the electronic switch means substantially constant while it isconducting.

A further object of this invention is to provide an ignition systemwherein current flow through the primary circuit is controlled by atransistor which is operated conductive or noncondu'ctive and wherein aconstantvo'ltage device such as a Zener diode is connected with thetransistor to maintain current flow through the transistor substantiallyconstant when. it is conductive.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing whereina preferred embodiment of the present invent-ion isclearly shown.

The single figure drawing is a schematic circuit diagram of an ignitionsystem made in accordance with this invention.

Referring now to the drawing, the reference numeral designates a storagebattery which is connected with the lead wire 12 and which has anopposite side connected directly to ground. The lead wire 12 isconnected with a generator 14 and this generator operates to charge-thebattery 10 and also operates to supply the other D.C. loads of the motorvehicle including the ignition system. The generator 14 is driven -bythe engine 16 of a motor vehicle and this generator may either be a DCgenerator or could be an A.C. generator fitted with diodes forrectifying the A.C. output of. the generator to direct current.

The lead wire 12 is connected to one side of a switch 18 and this switchcontrols the current flow to a cranking motor 20. The cranking motor 20is. operative to crank the engine 16 when it is desired to start theengine.

The lead wire 12 is connected to one side of an ignition switch 22, theopposite side of this switch being connected with lead wire 24. The leadwire 24 is connected with junction 26 and this junction is connected toa breaker contact 28 which cooperates with the breaker contact 30located on a breaker arm 3-2. Thebreaker arm 32 is electricallyconnected to one side of a resistor 34 and an opposite side of thisresistor is connected with a lead wire 36. The breaker contacts 28 and30 open and close in synchronisrn with operation of the engine 16 byvirtue oi? the connection of the'engine 16 with a breaker cam 38. Thebreaker cam, of course, causes the opening and closing of the breakercontacts 28 and 30 in a manner well known to those skilled in the art.

The lead wire 24 is connected to one side of a resistor 40, the oppositeside of this resistor being connected with the primary winding 42 of anignition transformer 44. The secondary winding 46 of the ignitiontransformer is connected with lead wires 48 and 50. The lead wire 50 isconnected with a lead wire 52 and it is seen that this lead wire isgrounded. The lead wire 48 is connected with a rotor contact 54 whichrotates in synchronism with the engine 16 and which passes by theelectrodes 56 formed in a distributor cap 58. Each of the electrodes 56is connected with a separate spark plug on the engine 16 and one ofthese spark plugs is designated by reference numeral .60. It is to beunderstood that there will be as many electrodes 56 as there are spankplugs, and therefore with a siXcy-1in der engine there will be siXequally spaced electrodes 56.

The ignition system of this invention includes an electronic switchmeans which in this case takes the form of an NPN transistor 62. Thecollector electrode of transistor '62 is connected directly to one sideof the primary winding 42 whereas the base electrode of transistor 62 isconnected with lead wire 64. The emitter electrode of transistor 62 isconnected with junction 66 and therefore is, grounded.

'The lead wire 64 is connected to one side of a variable resistor 68,the opposite side of thisresistor being connected with the junction 70.The junction 70 is condescribed, and when it is desired to start theengine 16,

the ignition switch 22 is closed and the switch 18 is closed to energizethe cranking motor 20. As the engine is cranked, the breaker contacts 28and 30 Will-be opened and closed by rotation of the breaker cam 38. Whenthe contacts 28 and 30 close, current will flow from one side of thebattery 10, through junction 26, through breaker contacts 28 and 30,through the dropping resistor 34, through variable resistor 68, and thenthrough the base to emitter junction of transistor 62 to ground. Currentwill now flow from one side of battery '10 through ignition switch 22,through lead wire 24, through resistor 40, through the primary winding42 of ignition transformer 44, and thence through the collector toemitter circuit of transistor 62 to ground. As the current flows throughthe primary winding 42, flux is built up in the ignition transformer. Asthe breaker contacts 28 and 30 open, there is no longer a circuitbetween junction 78 and the battery 10, and the base and emitterelectrodes of transistor 62 are connected through resistors 68 and 72.This will cause an abrupt turning off of the transistor 62 in itsemitter-collector circuit and will therefore cause a high voltage to beinduced in the secondary winding 46 of the ignition coil 44. This highvoltage is impressed across a spark plug 60 through a circuit thatincludes lead wire 48, rotor contact 54, one of the contacts 56 ofdistributor cap 58 and the lead wire connecting one of the electrodes 56Wtih the spark plug. After the engine starts switch 18 is opened and theignition system continues to operate in a manner just described.

It is pointed out that the Zener diode 76 performs a very importantfunction in the ignition system of this invention in that it maintains aconstant current through the primary circuit of the ignition system eventhough the system voltage may vary. Since a Zener diode is a constantvoltage device, it is apparent that the junction 78 will be maintainedat some voltage which is constant with respect to the voltage of leadwire 52 as long as the system voltage is higher than the Zener rating ofthe Zener diode. The circuit constants are such that the system voltagewill not go below the Zener rating of the Zener diode under normaloperating conditions. Since the junction 78 is maintained at a constantvoltage with respect to lead wire 52 when system voltage exceeds thevoltage rating of the Zener diode, the voltage applied between the baseand emitter electrodes of transistor 62 is maintained constant. Thus,with this arrangement the collector to emitter current of transistor 62will build up to a constant value and the current flow through theprimary winding 42of the ignition coil is therefore maintained constant.

It can be seen from the foregoing that changes in voltage within limitsbetween junction 26 and ground will not operate to change the primarycurrent flowing through the primary winding of the ignition coil andthis current will be maintained constant as long as system voltageexceeds the voltage rating of the Zener diode. In addition, a very finecontrol of primary current is achieved which will compensate for smallchanges in system Voltage.

The resistor as is made variable so that differences in individualtransistors may be compensated. This resistor will also compensate forthe change in gain characteristic of the transistor due to temperaturechanges.

The resistor 46 is optional and when used performs the function oflimiting current through primary winding of the ignition coil to adesired value at the lowest expected system voltage.

In the system as disclosed, a pair of breaker contacts 23 and 39 havebeen shown for varying the base voltage of the transistor 62 insynchronism with operation of the engine 16. It will be apparent tothose skilled in the art that any other device might be used to controlthe conductivity of the transistor 62 in timed relationship withoperation of the engine without departing from the spirit and scope ofthis invention.

While the embodiments of the present invention as herein disclosedconstitute a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. An ignition system for controlling the firing of a spark plug of aninternal combustion engine comprising, an ignition transformer having aprimary winding and a secondary winding, means connecting said secondarywin-ding with said spark plug, a source of direct current voltage whichmay fluctuate under different conditions of operation, a series circuitconnected across said source of voltage including the primary winding ofsaid ignition transformer and a first switching means, a secondswitching means operating in synchronism with said engine controllingsaid first switching means, and means connected in series with saidsecond switching means for maintaining a constant current flow throughthe primary winding of said ignition coil and through said firstswitching means when said first switching means is conductive andregardless of changes in voltage of said voltage source within apredetermined range.

2. An ignition system for an internal combustion engine comprising, anignition coil having a primary winding, a source of direct currentvoltage which may fluctuate under different conditions of operation, acircuit for energizing said primary Winding from said voltage sourceincluding in a series connection said primary winding and theemitter-collector circuit of a transistor,'means for causing a varyingvoltage to be applied across the emitter base circuit of said transistorin timed relationship with operation of said engine, said voltagevarying substantially between zero and a higher value, and means formaintaining said voltage substantially constant when it is at its highervalue and within a range of voltages of said voltage source.

3. An ignition system for an internal combustion engine comprising, anignition coil having a primary Winding, a source of direct currentvoltage which may vary under different conditions of operation, acircuit for energizing said primary winding including said voltagesource and the emittencollector circuit of a transistor, said transistorhaving a base electrode, means for applying a voltage to said baseelectrode of said transistor which varies between two values in timedrelationship with operation of said engine, and means for maintainingone of said values substantially constant regardless of changes involtage of said voltage source within a predetermined range.

4. An ignition system for an internal combustion engine comprising, anignition coil having a primary winding, a source of direct currentvoltage which may fluctuate under different conditions of operation, atransistor having emitter, base and collector electrodes, meansconnecting said primary winding and the emitter-collector circuit ofsaid transistor across said voltage source, means operating in timedrelationship with said engine for applying a varying voltage across theemitter and base electrodes of said transistor, said voltage varyingsubstantially between zero and a higher value, and a voltage limitingdevice connected across said emitter and base electrodes thereby theemitter to base voltage, when at its higher vxalue, has a substantiallyfixed value.

5.'An ignition system for an internal combustion engine comprising, anignition coil having a primary winding, a transistor having emitter,base and collector electrodes, a source of direct current voltage whichmay fluctuate under different conditions of operation, a first circuitconnected across said source of voltage including said primary windingand the emitter-collector circuit of said transistor, a pair of breakercontacts opened and closed in timed relationship with operation of saidengine, a second circuit connected across said voltage source includingsaid breaker contacts and the emitter-base circuit of said transistor,and a constant voltage device connected across the emitter and baseelectrodes of said transistor in series with said breaker contacts.

6. The system according to claim 5, whereln the constant voltage deviceis a Zener diode.

7. An electrical system comprising, a source of direct current voltagewhich may vary, an electrical load, a transistor having emitter,collector and base electrodes, a circuit for energizing said electricalload including said voltage source, and the emitter-collector circuit ofsaid transistor, means for varying the voltage applied to the baseelectrode of said transistor between two values, one of said valuescausing a conductivity of said transistor in its emitter-collectorcircuit and the other voltage value causing said transistor to besubstantially nonconductive in its emitter-collector circuit, and meansconnected with the emitter and base electrodes of said transistor forcausing the current fiow through said transistor to be substantiallyconstant Within a range of voltages of said voltage source when saidtransistor base electrode has a voltage value to cause it to beconductive.

8. An electrical system comprising, a source of direct current voltagewhich may vary, an electrical load, a transistor having emitter, baseand collector electrodes, an electrical circuit connecting said voltagesource and said load including the emitter-collector circuit of saidtransistor, means connected between the base electrode of saidtransistor and said voltage source for varying the potential applied tothe base electrode of said transistor between two values, one of saidvoltage values causing said transistor to be substantially fullynonconductive and the other voltage value causing said transistor to beconductive, and a constant voltage device connected with said baseelectrode for causing the voltage applied to said base electrode to besubstantially constant at one of said voltage values within apredetermined range of voltages of said voltage source.

9. An electrical system comprising, a source of direct voltage, anelectrical load, a transistor having emitter, base and collectorelectrodes, a circuit for energizing said electrical load from saidvoltage source including the emitter-collector circuit of saidtransistor, switch means, means connecting said switch means between thebase electrode of said transistor and said voltage source, meanspermanently connecting the emitter and base electrodes of saidtransistor, and a Zener diode connecting the emitter and base electrodesof said transistor, said Zener diode being connected in series with saidswitch means.

10. An electrical system comprising, a pair, of terminals adapted to beconnected across a source of direct current voltage, an electrical load,a first series circuit connecting said terminals including saidelectrical load and the emitter-collector circuit of a transistor,switch means, a second electrical circuit connecting said terminalsinclud ing said switch means and the emitter-base circuit of saidtransistor, a resistive circuit permanently connecting said emitter andbase electrodes of said transistor, and a Zener diode connected acrossthe emitter and base electrodes of said transistor in series with saidswitch means.

11. A transistor switching circuit comprising, a source of directcurrent, an electrical load, a transistor having emitter, base andcollector electrodes, a circuit for energizing said electrical load fromsaid source of direct current including the emitter and collectorelectrodes of said transistor, means connected across the emitter andbase electrodes of said transistor for applying a variable DC. voltageacross said emitter and base electrodes, said,D.C. voltage varyingbetween first and second values which are capable of driving saidtransistor substantially conductive and nonconductive between itsemitter and collector electrodes, and means for maintaining said voltagesubstantially constant when it is at said first value.

12. A transistor switching circuit comprising, a source of directcurrent, an electrical load, a transistor having emitter, collector andbase electrodes, a circuit for energizing said electrical load from saidsource of direct current including the emitter and collector electrodesof said transistor, a resistor connected across the emitter and baseelectrodes of said transistor, a control means connected in series withsaid resistor for causing a variation in current flow through saidresistor, said variation in current flow causing a voltage to bedeveloped across said resistor which has at least two values one ofwhich is capable of biasing said transistor to its conductive state, andmeans connected in parallel with said resistor for maintaining saidvoltage substantially constant when it biases said transistor to itsconductive state.

References Cited by the Examiner UNITED STATES PATENTS 2,939,018 5/1960Faulkner 30788.S 2,966,615 12/1960 Meyer 315-206 GEORGE N. WESTBY,Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

1. AN IGNITION SYSTEM FOR CONTROLLING THE FIRING OF A SPARK PLUG OF ANINTERNAL COMBUSTION ENGINE COMPRISING AN IGNITION TRANSFORMER HAVING APRIMARY WINDING AND A SECONDARY WINDING, MEANS CONNECTING SAID SECONDARYWINDING WITH SAID SPARK PLUG, A SOURCE OF DIRECT CURRENT VOLTAGE WHICHMAY FLUCTUATE UNDER DIFFERENT CONDITIONS OF OPERATION, A SERIES CIRCUITCONNECTED ACROSS SAID SOURCE OF VOLTAGE INCLUDING THE PRIMARY WINDING OFSAID IGNITION TRANSFORMER AND A FIRST SWITCHING MEANS, A SECONDSWITCHING MEANS OPERATING IN SYNCHRONISM WITH SAID ENGINE CON-